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Monday, August 30, 2010

Cyphostemma juttae, Vitaceae

About 20 years ago a South Africa botanist gave me a few seeds of this strange succulent, Cyphostemma juttae, which grows in rocky, arid parts of Namibia. It has taken all that time for the seedling to reach this size - about 70 cm. tall - on my windowledge and since it can grow to 2.5 metres tall in the wild it's still got some way to go, although it's under less than ideal conditions, in a flower pot.. Every winter it sheds those succulent leaves completely, leaving only the swollen stem - known botanically as a caudex - then regrows leaves in late spring. It first flowered about five years ago, but this is the first year that the flowers have produced fruits.

The stem constantly sloughs off layers of papery epidermis, which I suspect might have some role to play in reflecting intense sunlight.

The thick, lobed succulent leaves have a saw-tooth margin and each leaf lobe is about 15cm. long.

These small, glassy beads appear on the underside of the leaves, soon after they've fully expanded.

I've yet to discover whether they are crystalline sugar or resin - I suspect they are the latter.

One of the most remarkable aspects of the plant is that it is in the grape family and is commonly known as the Namibian grape or tree grape. You'd never suspect that until you take a look at the fruits, which turn purple when they ripen, but unlike the edible grape they are poisonous.

Thursday, August 19, 2010

Saponaria officinalis, Soapwort and Quinoa Chenopodium quinoa

If you are looking for a plant that has good credentials for inclusion in a wildlife garden, then soapwort Saponaria officinalis comes close to being a strong candidate - but with one serious drawback. In my experience its rapidly-elongating rhizomes make it very invasive.

Back in 1999 a trial of 25 native plant species carried out at the University Botanic Garden at Cambridge ranked soapwort was the second most popular nectar source for butterfly species,  with a very high nectar secretion rate and second only to purple loosestrife Lythrum salicaria in the number of butterfly species that it attracted. Not only that - it's also virtually slug-proof. Recently researchers in Poland have shown that slugs avoid eating soapwort.

Soapwort's slug-deterrent properties are due to compounds called saponins in its rhizomes and leaves. Shred some leaves, pour boiling water over them, give the resulting extract a good shake in sealed jam jar and you get this lovely frothy lather. Saponins are natural detergents, found in many plants including horse chestnut seed ('conkers'). A few years ago some Austrian research showed that slugs will not cross a barrier of ground-up conker seed meal and theoretically sprayed saponin extracts have the potential to protect seedlings that are susceptible to slug damage, but for the fact that saponins are very soluble and wash away in the rain.

Saponins are also present in quinoa Chenopodium quinoa seeds, a popular high protein grain with an excellent amino acid balance, sold in vegetarian and health food stores. They illustrate one of the great paradoxes of crop domestication, which often removes plants' natural defences and then must find alternative means for protecting crops from pests.

Quinoa is a very ancient crop from the Andes and the seeds need to be soaked in a couple of changes of water to remove the soluble saponins, which are mildly toxic to humans. Most quinoa seeds marketed for human consumption today should have been pre-washed but anyone growing it (quinoa can be cultivated in the UK - the above trial crop was photographed in Durham) should be careful to soak the seeds in at least two changes of water before consumption.  In the wild the bitter saponins are natural bird deterrents, so birds tend to leave those easily accessible, exposed seeds heads alone but attempts to breed more palatable saponing-free quinoa have produced crops that are rapidly devasted by birds. As is the case with many domesticated food crops, there is a conflict between breeding cultivars to remove anti-nutritional defensive compounds and protecting crops from pests. In order to make many crops edible for humans we need to weaken their natural chemical defenses and then must resort to alternative pesticides of one kind or another to combat the pests and diseases that inevitably attack: such is the treadmill of agriculture.   
Soapwort's saponins have been used for washing people and clothes for centuries. By all accounts an extract in hot water makes a fine shampoo, although I have to say that the extract smells like boiled cabbage so you'd need to rinse your hair very well afterwards and maybe scent the water with rosemary (as my grandmother used to do when she washed her hair). Soapwort extracts are also still used by conservators as gentle detergents to cleanse delicate fabrics and are reported to have been used to clean the Bayeaux tapestry.

You can read an interesting article about the origin of soaps, including saponins from soapwort here.

Saturday, August 14, 2010

Punica granatum, Pomegranate

A ripe pomegranate fruit is a natural object of great beauty - as are its seeds, with their succulent juicy aril, when they are scattered like jewels over a salad. There are few fruits that have a richer store of mythology associated with them. In antiquity they were associated with fertility, due to their numerous seeds and the ease with which these germinate. It’s easy to grow pomegranate as an attractive conservatory plant by sowing a few seeds, then training the resulting plants on a single stem and shortening the shoots in the crown of the plant, to produce a compact head of foliage bearing attractive, waxy scarlet flowers – but usually no fruits in Britain.

Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz, 1885, Gera, Germany

Pomegranate originates from northern Iran but by Roman times its popularity as a thirst-quenching fruit meant that it had spread around the Mediterranean. The Romans imported what they considered to be the finest fruits from Carthage, which they called Punica and which has provided the plant with its generic name. Pomegranates were widely grown in Roman villas and there are frescoes in the House of the Fruit Orchard in Pompeii dating from AD79 which depict the tree in fruit. According to Roman mythology, pomegranates are indirectly responsible for winter. In one version of the story Proserpina, daughter of Jupiter and Ceres (the goddess of the harvest), was abducted by Pluto and dragged into the underworld. In anger, Ceres froze the harvest and paced the earth, leaving desert wherever she travelled. Jupiter’s messenger Mercury eventually persuaded Pluto to let Proserpina go, but not before she had eaten six pomegranate seeds, the food of the dead, condemning her to live six months of the year with Pluto, during which time crops above withered in the winter, but when she returned to earth for the remaining six months she brought spring with her.

Dante Gabriel Rossetti. Prosperpine (1874). Tate Gallery London
Image source: Wikipedia

By the 4th. century AD the fruit had acquired Christian symbolism, with the many seeds within the fruit representing the followers of the church. There is a wonderful mosaic from a Roman villa at Hinton St. Mary in Dorset depicting Christ flanked by two pomegranates, which by then had become symbols of Christian devotion. Catherine of Aragon, the first wife of Henry VIII adopted the pomegranate, with its crown-like shape, as her badge and the fruit features in historical and literary associations in Spain.

There is only one other species of pomegranate, P. protopunica, an endemic on the island of Socotra, and Punica is the only genus in the family Punicaceae.

Wednesday, August 4, 2010

Alocasia amazonica

Any plant with the specific name amazonica always has an air of the exotic about it, but the truth is that this attractive houseplant has no links with the Amazon or South America. Strangely, it's sometimes known as elephant's ears or African mask plant - and it has no links with Africa, either. It's a hybrid between two species from the other side of the planet, A. sanderiana from the Philippines and A. lowii from Borneo. I've no idea why it acquired the epithet amazonica. It makes a very striking houseplant , although once it blooms it tends to lose some of its symmetry. I always think that cowled inflorescence and ribbed, shield-shaped leaf give it an air of menace; it has a hint of voodoo or witchcraft about it, which I guess is where the name African mask plant originated.